Field of the Invention
This invention relates to color cathode ray picture tubes, and is addressed specifically to an improved shadow mask blank for use in the manufacture of color tubes having shadow masks of the tension foil type mounted in association with a substantially flat faceplate. The invention is applicable in color tubes of various types, including those used in home entertainment television receivers, and in medium-resolution, high-resolution, and ultra-high resolution tubes intended for color monitors.
The use of the tension foil mask and flat faceplate provides many benefits when compared to the conventional domed shadow mask and correlatively curved faceplate. Chief among these is a greater power-handling capability which makes possible as much as a three-fold increase in brightness. The conventional curved shadow mask, which is not under tension, tends to "dome" in picture areas of high-brightness where the intensity of the electron beam bombardment is greatest. Color impurities result as the mask moves closer to the faceplate and as the beam-passing apertures move out of registration with the phosphor deposits. The tension foil mask will not dome, but the heating effect of the electron beams on the mask can exert another undesired effect on the thin metal foil in that the foil can wrinkle, especially in corner areas. Such wrinkling can have a deleterious effect on picture tube resolution and color purity.
The tension foil shadow mask is a part of the cathode ray tube front assembly, and is located in spaced adjacency to the faceplate. The front assembly comprises the faceplate with its screen consisting of deposits of light-emitting phosphors, a shadow mask, and support means for the mask. As used herein, the term "shadow mask" means an apertured metallic foil which may, by way of example, be about 0.001 inch thick, or less. The mask must be supported in high tension a predetermined distance from the inner surface of the cathode ray tube faceplate; this distance is known as the "Q-distance." As is well known in the art, the shadow mask acts as a color-selection electrode or parallax barrier which ensures that each of the three beams projected by the electron gun lands only on its assigned phosphor deposits on the screen.